Energy-efficient Germanium electro-absorption modulator for ‘Green’ photonics applications

In this work, we have developed a Ge electro-efficient (EA) modulator whereby light is coupled evanescently from a crystalline silicon waveguide up into a Ge rib. A lateral electric field is employed in the Ge rib to enhance absorption via the Frank-Kedlysh effect which enables light modulation. The EA effect is most pronouced at wavelengths beyond 1580 nm due to a roll-off in absorption coefficient. With a small active area of 16 μm² (Device length of 40 μm), an extinction ratio of larger than 8 dB could be achieved for a wavelength range of 1580-1620 nm. The energy consumption of the modulator is typically less than a pico Joule per bit (assuming a 1 Gbps bit rate), and can be as low as tens of femto Joules per bit, depending on the device dimension and operating condition. Furthermore, our proposed EA modulator structure enables ease of integration for evanescent-coupled Ge-based EA modulator and photodetector, offering a more feasible monolithic integration scheme for these active devices.